Mauna Loa & How it Was Made

What is Mauna Loa?

Mauna Loa, “long mountain,\" is the world’s largest volcano. When measured from it’s base below sea level, Mauna Loa is actually more than three-quarters of a mile taller than Mount Everest. Mauna Loa is one of Hawaii’s five main volcanoes that make up the Pacific island chain. It began erupting more than 700,000 years ago, but as of 2009, the volcano has been inactive for 25 years.

Prehistoric Beginnings: Under-Sea Formation

Mauna Loa originally was formed deep under the Pacific Ocean by hot magma deep below the earth’s surface. An 80-million-year-old, 3,600-mile-wide volcanic hot spot exists below the Hawaiian chain of volcanoes, and Mauna Loa is one of the five Hawaiian volcanoes fed by this hot spot. As the lava came into contact with the Pacific Ocean, it cooled and hardened. Over time, the deposits of lava increased the level of the ocean floor until a sea mount formed. As lava built up for hundreds of thousands of years, the mount eventually broke the surface of the ocean and formed an island.

Above-Sea Formation

About 400,000 years ago, the first above-water land mass of Mauna Loa appeared above the surface of the Pacific Ocean. Mauna Loa is considered a “shield” volcano,\" which means that it was formed from lava that oozes slowly from fissures in the earth. This differs from cascade volcanoes, which can shoot violently upward with little warning such as Mt. Etna or Mt. St. Helens.

Recent Seismic Activity

Mauna Loa is home to several hot spots, or places where an abundance of heat is centered in one location. Within the last 100 years, Mauna Loa lava flows have caused multiple catastrophic events on the island. In 1926, the village of Ho??p?loa Makai was destroyed when the largest eruption in recent history overtook the area. In June 1950, the village of Ho?okena Mauka also was destroyed in similar fashion. Eruptions in 1975 and 1984 were significant, although they caused far less damage than past events.

In 2002, seismic inflation increased along the walls of Mauna Loa below the surface. In July 2004, several deep earthquakes began, lasting until the end of that year. For the first three weeks, an earthquake was reported daily and the number increased steadily until December 2004 when they ended.